1. Field of the Invention
This invention relates to methods and control systems for registering a datum position between two relatively movable components of a machine tool.
2. Background Prior Art
U.K. Patent Publication No. 2,164,444 discloses a position monitoring apparatus for monitoring back and forth travel between two relatively rotatable or linearly movable components. One component carries an interrupter and the other component carries a detector unit. The interrupter has projecting parts at predetermined positions, and the passage of the these parts past the detector unit is detected to monitor the relative position. The detector and the interrupter act via a logic circuit to identify datum position and to identify which side of the datum position the components lie and also to identify when the components are approaching the ends of the range of travel in order to bring movement to a stop in a home position at each end of the range of travel.
U.K. Patent Publication No. 2,171,196 discloses a detecting means for detecting the setting of an adjustable member such as a vehicle flap or rudder. The detecting means comprises a light source which emits parallel light and the emitted light beam of which is split into a measurement and a reference beam. These beams are conducted through respective fibre-optic cables which extend to the member and back to respective light-sensitive elements arranged in the vehicle. The cable for the measurement beam includes, in the proximity of the flap, an optical stop which acts as a displacement angle pick-up and the light passage area of which is variable in dependence on the setting of the flap. The cable for the reference beam may include an optical reference stop, the light passage area of which is variable by a setting motor in dependence on the difference between the output signals of the elements until this difference is zero. The motor can be coupled with equipment for determining the setting of the flap from the displacement of the reference stop.